The Ratioflo® Volumetric Module (RVM) has two basic moving elements...
(1) the Double Acting Free-Piston and (2) the Flow Control Valve.

The functional sequence is as follows:

Liquid under pressure enters the inlet port of the Module causing the piston to travel up or down, depending upon the position of the valve, and an equal volume of product is discharged from the outlet port. As the piston reaches its upper stroke limit, the magnetic reed switch (MRS) senses the ring magnet on the piston and signals the valve to shift 90 degrees counter-clockwise (CCW). (For single stroke operation this would signal the end of the cycle, and the valve would not shift until the next cycle)

The internal flow action is now reversed. The product entering the Module is directed up through the central co-axial tube causing the piston to go down... the product beneath the piston is discharged directly to the outlet port.

The piston will remain at the lower end of the Module until the valve is again actuated 90 degrees CW. Note that the flow stops when the piston stops. The lower magnetic reed switch (MRS) also senses that the piston stroke has been completed; thus, the signal can be used to shift the valve to continue operation or, otherwise, indicate that the cycle has been completed.